Why doesn't someone with competence and time to kill code the process onto an SD card to sell on ebay?

The nag screen isn't much of an annoyance - not enough to prompt me to follow the instructions and turn the danged thing off myself, but it IS enough annoyance that I'd pay thirty bucks for an SD card I could plug in and let the AVIC update itself ...

(AVIC Z110BT, updated with 2012 maps/firmware).

At $30 a pop plus the cost of an SD card, how many do you have to sell to make it worth your time? And how many people are going to pay $30 for something they can get fo free? It takes all of 5 minutes tops and the how to guides are readily available. Laziness? I think yes. Anyone can learn.

It is also highly version dependent.  If you modify the wrong location in the code you'd end up with problems.